There exist various technological solutions for amplifying and/or reducing the pressure of a hydraulic circuit. Note that it is technologically more difficult to amplify or to reduce the pressure of a hydraulic flow that must be continuous than to amplify or to reduce the pressure of a hydraulic flow where a discontinuous flow is acceptable.
The dominant principle on which most pressure amplifiers or reducers rely consists in a sender piston rigidly connected to a receiver piston, said two pistons moving over the same stroke and having different sections. In this case, each piston cooperates with a cylinder and a head while the sender piston communicates with a hydraulic circuit independent of that of the receiver piston. To increase the pressure, the sender piston must have a larger section than the receiver piston, whereas to reduce said pressure the sender piston must have a section smaller than that of the receiver piston. According to this principle, the average flow rate of the hydraulic circuit at the lower pressure is greater than the average flow rate of the hydraulic circuit at the higher pressure.
The advantage of pressure amplifiers or reducers employing pistons as just described is their simplicity, their compactness, their low unit cost, and their high efficiency provided that said pistons make a good seal with the cylinder with which they cooperate. On the other hand, their principal disadvantage is their pulsed operation and, to a lesser degree, the fact that they cannot recover all of the compression energy of the hydraulic fluid, particularly on the sender piston side.
Another pressure amplifier or reducer configuration consists in a first sender rotary positive displacement hydraulic pump and a second receiver rotary positive displacement hydraulic pump having a different cubic capacity, said pumps being mounted on the same shaft or at least synchronized in rotation by a transmission of any kind. In accordance with said other configuration, the pistons of the pressure amplifiers or reducers employing pistons are replaced by said pumps, which can be of any type known to the person skilled in the art.
The advantage of pressure amplifiers or reducers employing rotary positive displacement hydraulic pumps essentially consists in improved continuity of the flow of the hydraulic fluid both on the high-pressure side and on the low-pressure side. Another advantage consists in the possibility of easier incorporation of a transmission defining different rotation ratios between the sender pump and the receiver pump. An alternative to this latter solution consists in providing for at least one of the two pumps to be of variable cubic capacity.
The problem of pressure amplifiers or reducers employing rotary positive displacement hydraulic pumps is their cost, their complexity, their overall size and their efficiency, which is generally lower than that of pressure amplifiers or reducers employing pistons.
Note that numerous pressure amplifiers or reducers employing opposed pistons intended to produce a virtually continuous flow have been patented. For example, note the published patent FR2889265, which provides a low-pressure piston referred to as the “differential piston” delimiting two low-pressure chambers and actuating two high-pressure pistons placed on respective opposite sides of said low-pressure piston, while a distributor includes a switching slide valve actuated by mechanical means actuated by the low-pressure piston, said means here being drive fingers that push on the low-pressure piston at the end of travel.
According to this configuration, each high-pressure piston constitutes, with its cylinder and with valves with which it cooperates, a high-pressure pump, the high-pressure pistons being moved in alternating longitudinal translation by the low-pressure piston, the faces of which are alternately and with opposite phase exposed to a low-pressure hydraulic pressure. It is clear that the low-pressure piston constitutes a low-pressure stage while the high-pressure pistons together produce a high-pressure stage.
It is also clear on reading the patent FR 2889265 that only pressure amplification is possible, the device providing no pressure reduction. In fact, according to said patent FR 2889265, the high-pressure stage can only be a receiver and not a driver because it in fact constitutes a pump.
Note the published patent FR2575792 which describes a hydraulic pressure amplifier functioning in an analogous manner except that the low-pressure piston has two different sections on each of its faces. In the first direction of movement of the low-pressure piston, only the smaller section face is exposed to a low-pressure hydraulic pressure while in the second direction of movement of said piston the larger section face produces an antagonistic force twice that produced by the smaller section face, said two faces remaining simultaneously exposed to the low-pressure hydraulic pressure. The result obtained is similar to that produced by the pressure amplifier employing opposed pistons protected by the patent FR 2889265. Apart from the particular configuration of its low-pressure piston, the patent FR 2575792 is distinguished from the patent FR 2889265 in that the reversing of the direction of movement of said piston is brought about by ports that said piston can block or open at the end of its stroke in order to maneuver in translation a switching slide valve, once again because of two opposed axial faces of different effective section that said slide valve exposes simultaneously or not to the low-pressure hydraulic pressure.
It is clear on reading the patent FR 2575792 that in this case also only pressure amplification is possible for reasons analogous to those that impose the same functional limitation on the device that the patent FR 2889265 describes.
The U.S. Pat. No. 5,984,026 relies on the same principle as the previous two patents, except for the detail that the switching slide valve is maneuvered both by mechanical means cooperating with the low-pressure piston and by the hydraulic pressure that exerts a force alternately on one or the other face of said slide valve which consequently moves the slide valve.
In this latter case also only pressure amplification is possible for reasons analogous to those that impose the same functional limitation on the devices described in the patents FR 2889265 and FR 2575792.
The patent EP0234798 describes other variants of the same principle and employs a low-pressure piston delimiting two low-pressure chambers to form a low-pressure stage, said piston actuating two high-pressure pistons placed on respective opposite sides of said low-pressure piston in a similar way to what is described in the previous three patents. Said patent EP0234798 this time employs a staggered low-pressure hydraulic fluid distributor that includes a primary switching slide valve actuated by mechanical means cooperating with the low-pressure piston while said slide valve controls the switching pressure applied alternately to the two axial faces of a secondary switching slide valve employing valves and valve seats.
Other variants described in the patent EP 0234798 notably consist in a switching slide valve driven in translation by a mechanical actuator the screw of which is rotated by a cable connected to the low-pressure piston.
Note that the variants of the patent EP 0234798 again relate only to the low-pressure stage of the pressure amplifier. The high-pressure stage in fact is still a hydraulic pump employing two opposed plunger pistons. These variants are therefore not reversible to enable pressure reduction, and the pressure amplifiers as described in the patents FR 2889265, FR 2575792 and U.S. Pat. No. 5,984,026 are not reversible either.
It is found that products are marketed that rely on these principles and that notably enable ultra-high-pressures to be generated from lower pressure sources. This applies, for example, to the company “Hydroprocess”, which offers pressure amplifiers employing a double-acting low-pressure piston actuating two high-pressure pistons placed on respective opposite sides of said low-pressure piston, which amplifiers can be used in water jet cutting systems, for example.
Note that the devices described are therefore only pressure amplifiers and not are reversible. This is because the high-pressure stage operates only as a pump and is not equipped with a switch, while the low-pressure stage is designed only to operate as a driver, its switching device not being intended to enable said low-pressure stage to operate as a pump.
Note moreover that the high-pressure stage would with difficulty accommodate switches employing slide valves or ports as employed in the various patents described above because the ultra-high-pressures usually required mean that any leakage at the level of the slide valves or ports compromises efficiency, whether said leaks occur during the maneuver to open or block said slide valves or ports or while the slide valves or ports are held closed, being by their nature imperfectly sealed at ultra-high-pressures. It would then be necessary to provide actuators employing valves, needle valves or ball valves because these devices are inherently fluid-tight, although they generate high maneuvering forces.